1. Field of the Invention
The present invention relates to read/write apparatuses, and more particularly to a read/write apparatus in which information is written to and read from a sector having a predetermined address, using a head associated with a target recording surface.
In most magnetic disk drives that are used recently, information is written to and read from a magnetic disk (recording medium) according to one of the following schemes: a servo surface servo method in which servo information and the like is written on a surface of a disk dedicated for servo information; and a data surface servo method in which servo information and the like is recorded on a data surface. The data surface servo method allows a reduction in the number of magnetic disks and an increased storage capacity. In either method, information is written to a data area in a predetermined sector. Servo information for positioning the corresponding head is recorded in a servo area. Information related to writing and reading (addresses, etc.) is recorded in an ID area.
Demand for further increases in storage capacity makes it necessary to consider the possibility of omitting the ID area, particularly in the data surface servo method. In this regard, it is necessary not only to transfer the information in the ID area to another area, but also to reduce the volume of information recorded.
2. Description of the Related Art
Conventionally, when a magnetic disk drive is used as a read/write apparatus for a host system such as a personal computer or other information processing apparatus, the host computer or other information processing apparatuses records using the magnetic disk drive by dividing data into 512-byte units. Addresses are written, as identification information for differentiating between 512-byte data from each other, in the ID area where information relating to writing and reading is recorded. Therefore, the ID area always precedes the corresponding 512-byte data area. When a reading or writing operation is performed, the ID area is always referred to immediately before the data area is accessed.
A magnetic disk drive is generally equipped with one or a plurality of magnetic disks, and a reading/writing head is provided for the recording surfaces of each of the magnetic disks. Switching between the heads in order to access the magnetic disk is effected by a head IC comprising a register or the like.
FIG. 1 explains a disk format according to the conventional data surface servo method. Referring to FIG. 1, a sector on each of the tracks of the magnetic disk consists of an ID area (ID) and a data area (DT). For convenience's sake, sequential numbers are allocated to the ID areas and the data areas such that an index mark provided as a reference point in the track is followed by numbers ID0, ID1, . . . , DT0, DT1, . . . . Synchronization codes (SB) are provided at the head of the ID area and the data area.
Thus, the ID area numbered ID0 corresponds to the first data block (data area DT0) of the track. Here, an address comprising a cylinder number, a head number and a sector number is written. Writing and reading in the data area DT0 is conducted after the ID area ID0 is accessed and the address therein is referenced. The ID area ID1 is an ID area for the next data block.
The servo information is written on a track at equidistant intervals. For example, servo information is written in a servo frame obtained by dividing the circumference into 40 or 60 areas. The servo information contains information for controlling the magnetic disk to be rotated at a precisely controlled cycle, and information necessary for a seek operation of the head. In some cases, the servo information may include a cylinder number.
Since the servo information is written on a track at equidistant intervals, a data area may be divided as indicated by data areas DT0, DT1, . . . in FIG. 1. The way data areas are divided may differ from one sector to another. For example, the Japanese Laid-Open Patent Application No. 2-71458 discloses a scheme whereby servo termination information for canceling a write inhibit signal is recorded at the end of the servo information so that the servo information is not mistaken for the data area and erased.
As described above, immediately before writing is performed in the data area, the address in the ID area is read so that writing is conducted in a data block of a proper sector.
It is possible to know the position of the sector accessed by performing a seeking operation of the head or by generating a sector pulse. However, these schemes do not have satisfactory reliability. The seek operation makes it possible to accurately know the position of the first cylinder 0 (track 00) using the guard band zone. Regarding the other tracks, the sought cylinder address is known by counting track crossing pulses generated when the head crosses from one track to another.
There may be missing track crossing pulses during the seek operation. Conversely, excessive track crossing pulses may be generated. Thus, there may be cases where the cylinder reached in the seek operation is different from the target cylinder.
There are similar problems with sector pulses. That is, servo mark signals may be missing or excessively generated. Since the seek control and the sector pulse generation are conducted by reading information recorded on the magnetic disk, missing or excessive track crossing pulses or servo mark signals occur as a result of a failure to read recorded patterns on the magnetic disk or a failure in detecting the information correctly.
Further, the head does not return a feedback signal that allows confirmation that the proper head has been selected.
Thus, providing an ID area ensures that the cylinder identifier, the head identifier and the sector address can be confirmed. In this way, it is possible to prevent writing and reading of data in a sector which is not a target area.
An arrangement wherein the ID area is omitted to meet a demand for an increased storage capacity does not serve the purpose because the information including the head identifier and the sector address that is conventionally recorded in the ID area has to be incorporated in the servo information, resulting in only a reallocation of the information. In this arrangement, in order to improve reliability, redundancy codes such as cyclic redundancy check (CRC) codes should be added to the servo information in which the address information is arranged. Otherwise, some information may be recorded multiple times. Thus, there is a problem in that the size of the servo information itself becomes large.
Further, incorporating the head information in the servo information means that different servo information should be recorded on different magnetic disk surfaces associated with respective heads. Thus, the recording of the servo information becomes complex.